In many geographical locations of the world there are more pumpjack units than there are people. These pumpjack units produce crude oil from a production formation located thousands of feet below the ground. Usually the pumpjack unit is supported on the ground adjacent the wellhead and actuates a sucker rod string that extends into the wellbore and downhole to a downhole production pump of the reciprocatory type.
Some of these wells are very old, and for one reason or another, are crooked and therefore the production tubing is curved into a sinusoidal wave pattern at several locations along its length. This meandering of the wellbore forces the sucker rod into engagement with the inner wall surface of the production tubing string, causing it to scrape or rub against the tubing string at a number of elevations as the rod is reciprocated by the horse-head of a pumpjack rocking beam. This scraping accelerates the wear between the outer surface of the sucker rod and the inner surface of the tubing string so that eventually either the rod will part or the tubing string will commence leaking production fluid into the wellbore annulus, and, for many different reasons, either of these conditions is considered highly undesirable and costly.
In the past, tubing rotators have been employed at the surface of the earth to rotate the tubing string respective to the rod and casing strings to thereby distribute the wear between the outer surface of the rod string and the inner surface of the tubing string as opposed to the wear being concentrated at one side of the rod and tubing string. This provides improved wear characteristics of the rod string and tubing string but it also requires that the lower end of the tubing string be left free to rotate and this brings about accelerated failure of several components of the production equipment for reasons other than the rubbing together of the sucker rod and tubing string. This accelerated failure of the production equipment components is a result of the pump plunger cyclically lifting the entire column of fluid up the tubing string several strokes each minute, which cyclically induces an upward force into the production tubing and thereby works or fatigues the multitude of connections located in the tubing. Consequently early failure of these and other production equipment components often results from this arrangement.
It is not unusual for the lower end of the tubing string to be anchored downhole and thereby straightens the tubing string into a sinusoidal wave pattern having less amplitude than an untensioned tubing string. This improved distribution of wear is helpful, but usually inadequate, and therefore it is desirable to further reduce the wear so that it is more evenly distributed between the sucker rod string and the tubing string.
Applicant has discovered that rotating the production tubing string respective to the sucker rod and casing string while concurrently placing the production tubing string in tension reduces the severity of wear of the curved tubing string by reducing the contact area between the tubing string and rod string and concurrently distributing the wear between the sucker rod string and the tubing string. This system of operation additionally reduces the cyclic working of the production string and thereby overcomes many of the above drawbacks while taking advantage of the recited benefits. Moreover, the unexpected benefit of enhancing the protection of the sucker rod and production tubing afforded by corrosion inhibitors is realized by continually moving the rod and tubing surface away from the contact area therebetween, thereby treating the surface of the rod and tubing string each rotation of the tubing string.
This novel and unobvious solution to the recited prior art problems, however, calls for a means by which the opposed ends of the tubing string can be rotatably anchored to thereby place the tubing string in tension while at the same time conveying production fluid into and up the production string and then away therefrom. Therefore, in order to achieve all of the above desired goals simultaneously, it is necessary to provide an upper fluid conveying sealed swivel for the upper end of the tubing string and to support and rotate the upper end of the tubing string respective to the wellhead, rod string, and casing string; and, for the rotatable tubing string to be connected to a downhole fluid conveying swivel and anchoring device so that the tension force in the lower end of the production tubing is transmitted into the lower borehole; all of which is further complicated by the necessity of being able to remove the lower swivel and anchoring device in order to service other subsurface equipment. Therefore, a method and apparatus must be provided by which the anchor device can selectively be released from the surface of the ground.
In the past this was achieved by rotating the tubing string counterclockwise to set the anchor device, and rotating the tubing string clockwise to release the anchor device. In the above example, however, the downhole swivel adjacent the anchor precludes the tubing string transmitting a torque to release the anchor device.
This invention provides an unobvious solution to the above problems by the provision of a unique combination by which a fluid conveying swivel, locking mechanism, and anchor device is actuated to set and release the anchor device in response to manipulation of the tubing string from the surface of the ground.
It is invention to rotatably suspend a tubing string from a wellhead and to place the tubing string in tension by releasably anchoring the lower marginal end of the tubing string to the interior of a well casing, and providing a downhole swivel at a location uphole of and near the anchor device; and, providing a rotating apparatus at the surface of the ground and means by which the lower swivel can be locked and unlocked by manipulating the tubing string from the surface of the ground.
The instant solutions to the old problem of crooked production wells is the subject of the present invention.